This project is examining auditory aberrations in multiple sclerosis patients through the use of an extensive battery of special auditory tests. Complementary information provided by detailed vestibular and neurological evaluations is employed to specify the site(s) of lesion or lesions within the CNS due to multiple sclerosis. During the past three and three-fourths years, 200 multiple sclerosis patients have been tested one or more times. (The investigative plan calls for repeated tests at 6 month intervals, or sooner if the disease process is fluctuating). Detailed analysis of the patients seen thus far in this project reveals little if any loss of hearing sensitivity in most of our subjects, but an unusual audiometric configuration is frequently seen. The hearing threshold curve is often arched with better sensitivity for mid-frequencies than for low or high frequencies. Among other findings, those of most interest are: marked threshold tone decay, frequently bilaterally; decruitment; unusual difficulty in understanding speech in white noise; and decreased release from masking for both 500Hz tones and for spondaic words. Some of the common (40-55 percent incidence) vestibular abnormalities are poor optokinetic, slow and pendulum tracking; positional nystagmus; hyperexcitability; poor attentuation; and unilateral paresis. Neurological evaluations provided clinical confirmation of CNS lesions in these subjects.